|Systematic (IUPAC) name|
|Trade names||Prozac, among others|
|Licence data||US FDA:|
|Pregnancy cat.||C (AU) C (US)|
|Legal status||Prescription Only (S4) (AU) ℞-only (CA) POM (UK) ℞-only (US)|
|Metabolism||Hepatic (mostly CYP2D6-mediated)|
|Half-life||1–3 days (acute)
4–6 days (chronic)
|Excretion||Urine (80%), faeces (15%)|
|CAS number||Y Y|
|Mol. mass||309.33 g·mol−1|
|Melt. point||179–182 °C (354–360 °F)|
|Boiling point||395 °C (743 °F)|
|Solubility in water||14 mg/mL (20 °C)|
|N (what is this?)|
Fluoxetine (also known by the tradenames Prozac, Sarafem, Ladose and Fontex, among others) is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class. Fluoxetine was first documented in 1974 by scientists from Eli Lilly and Company. It was presented to the U.S. Food and Drug Administration in February 1977, with Eli Lilly receiving final approval to market the drug in December 1987. Fluoxetine went off-patent in August 2001.
Fluoxetine is approved in the US for the treatment of major depression (including paediatric depression), obsessive-compulsive disorder (in both adult and paediatric populations), bulimia nervosa, panic disorder and premenstrual dysphoric disorder. In addition, fluoxetine is used to treat trichotillomania if cognitive behaviour therapy is unsuccessful. In combination with the atypical antipsychotic olanzapine it is known by a few brand names,[note 1] including its US brand name Symbyax, which is approved for the treatment of depressive episodes as part of bipolar I disorder and in the treatment of treatment-resistant depression.
Despite the availability of newer agents, fluoxetine remains extremely popular. In 2010, over 24.4 million prescriptions for generic formulations of fluoxetine were filled in the United States alone, making it the third most prescribed antidepressant after sertraline (SSRI; became generic in 2006) and citalopram (SSRI; became generic in 2003). In 2011, 6 million prescriptions for fluoxetine were handed out in the UK.
Fluoxetine is frequently used to treat major depression, obsessive compulsive disorder, post-traumatic stress disorder, bulimia nervosa, panic disorder, body dysmorphic disorder, premenstrual dysphoric disorder, and trichotillomania. A recent clinical trial found that in bipolar II disorder fluoxetine was equally effective as lithium in preventing future mood episodes. It has also been used for cataplexy, obesity, and alcohol dependence, as well as binge eating disorder. Fluoxetine has also been tried successfully a treatment for autism.
Fluoxetine was shown to be effective for depression in six-week-long double-blind controlled trials, where it also alleviated anxiety and improved sleep. Fluoxetine was better than placebo for the prevention of depression recurrence when the patients, who originally responded to fluoxetine, were treated for a further 38 weeks. Efficacy of fluoxetine for geriatric, as well as pediatric, depression was also demonstrated in placebo-controlled trials. However two meta-analyses of randomized placebo-controlled trials suggested that in patients with mild or moderate symptoms, the efficacy is clinically insignificant. It has also been argued that any improvements in mood found in trials for fluoxetine (and other SSRIs) are simply a product of an exaggerated placebo effect, regardless of the severity of depression.
Research suggests that a significant part of the resistance to the SSRIs paroxetine (Paxil) and citalopram (Celexa) can be explained by the genetic variation of Pgp transporter. Paroxetine and citalopram, which are Pgp substrates, are actively transported from the brain by this protein. Fluoxetine is not a substrate of Pgp, and thus a switch from paroxetine or citalopram to fluoxetine may be beneficial to the nonresponders.
OCD was successfully treated by fluoxetine in two adult and one pediatric placebo-controlled 13-week trials. The higher doses of fluoxetine appeared to result in better response, while the reverse relationship was observed in the treatment of depression. Fluoxetine dramatically, by 40–50%, decreased the frequency of panic attacks in two controlled trials of panic disorder patients. In three double-blind trials, fluoxetine significantly decreased the number of binge-eating and purging episodes of bulimia nervosa. Continued year-long treatment of the patients, who originally responded to fluoxetine, was more effective than placebo for the prevention of bulimia nervosa episodes.
In children and adolescents fluoxetine is the antidepressant of choice due to the relative abundance of evidence favouring its efficacy and its favourable tolerability profile. In pregnancy fluoxetine's use is advised against, the evidence supporting an increased risk of major foetal malformations resulting from fluoxetine exposure is limited, although the MHRA of the UK has warned prescribers and patients of the potential for fluoxetine exposure in the first trimester (during organogenesis, that is the formation of the foetus' organs) to cause a slight increase in the risk of congenital cardiac malformations in the newborn. Although an associated between fluoxetine use during the first trimester and an increased risk of minor foetal malformations was been observed in one study. Sertraline is usually the preferred SSRI during pregnancy due to the relatively minimal foetal exposure observed. It is secreted in breast milk and hence it is advised that nursing mothers taking fluoxetine should not breastfeed their children.
Adverse effects by incidence
Very common (>10% incidence) adverse effects include:
Common (1-10% incidence) adverse effects include:
Uncommon (0.1-1% incidence) adverse effects include:
Rare (0.01-0.1% incidence) adverse effects include:
Very rare (<0.01% incidence) adverse effects include:
Unknown frequency adverse effects include:
Fluoxetine is considered the most stimulating of the SSRIs (that is it is most prone to causing insomnia and agitation). It also appears to be the most prone of the SSRIs for producing dermatologic reactions (e.g. urticaria (hives), rash, itchiness, etc.). Chronic SSRI treatment may also be associated with deficits in concentration and intellectual ability. Flattening of affect can also occur in an otherwise successfully treated with SSRIs patient, whether or not this is due to the drug or the underlying depression is yet to be determined. The aforementioned sexual side effects, although usually reversible, can persist for months, years, or permanently after the drug has been completely withdrawn. This is known as Post SSRI Sexual Dysfunction.
Several case reports in the literature describe severe withdrawal or discontinuation symptoms following an abrupt interruption of fluoxetine treatment. However, various studies have shown that the side effects of the fluoxetine discontinuation are uncommon and mild, especially compared to paroxetine, venlafaxine and fluvoxamine, probably due to the relatively long pharmacological half-life of fluoxetine. One of the recommended strategies for the management of discontinuation syndrome with other SSRIs is to substitute fluoxetine for the original agent, in cases where tapering off the dose of the original SSRI is ineffective. The double-blind controlled studies support this opinion. No increase in side effects was observed in several studies when the treatment with fluoxetine was blindly interrupted for a short time (4–8 days) and then reinstated, this result being consistent with its slow elimination from the body.
More side effects occurred during the interruption of sertraline (Zoloft) in these studies, and significantly more during the interruption of paroxetine. In a longer, 6‑week-long, blind discontinuation study, an insignificantly higher (32% vs 27%) overall rate of new or worsened side effects was observed in the group that discontinued fluoxetine than in the group that continued treatment. However, a significantly higher 4.2% rate of somnolence at week 2 and 5–7% rate of dizziness at weeks 4–6 were reported by the patients in the discontinuation group. This prolonged course of the discontinuation symptoms, with dizziness persisting to the end of the study, is also consistent with the long half-life of fluoxetine in the body. According to a 2007 summary report of available evidence, fluoxetine has the lowest incidence of discontinuation syndrome among several antidepressants including paroxetine and venlafaxine.
The FDA now requires all antidepressants to carry a black box warning stating that antidepressants may increase the risk of suicide in people younger than 25. This warning is based on statistical analyses conducted by two independent groups of the FDA experts that found a 2-fold increase of the suicidal ideation and behavior in children and adolescents, and 1.5-fold increase of suicidality in the 18–24 age group. The suicidality was slightly decreased for those older than 24, and statistically significantly lower in the 65 and older group. This analysis was criticized by Donald Klein, who noted that suicidality, that is suicidal ideation and behavior, is not necessarily a good surrogate marker for completed suicide, and it is still possible that antidepressants may prevent actual suicide while increasing suicidality.
There is less data on fluoxetine than on antidepressants as a whole. For the above analysis on the antidepressant level, the FDA had to combine the results of 295 trials of 11 antidepressants for psychiatric indications to obtain statistically significant results. Considered separately, fluoxetine use in children increased the odds of suicidality by 50%, and in adults decreased the odds of suicidality by approximately 30%. Similarly, the analysis conducted by the UK MHRA found a 50% increase of odds of suicide-related events, not reaching statistical significance, in the children and adolescents on fluoxetine as compared to the ones on placebo. According to the MHRA data, for adults fluoxetine did not change the rate of self-harm and statistically significantly decreased suicidal ideation by 50%.
Psychiatrist David Healy and certain patient activist groups have compiled case reports of violent acts committed by individuals taking fluoxetine or other SSRIs, and have argued that these drugs predispose susceptible individuals to commit violent acts.
Serial case report studies of this type have been criticized as being subject to "confounding by indication", in which effects due to an underlying disease state are mistakenly attributed to the effects of treatment. Other studies, including randomized clinical trials and observational studies, have suggested that fluoxetine and other SSRIs may reduce the propensity for violence. A randomized clinical trial performed by the US National Institutes for Mental Health found that fluoxetine reduced acts of domestic violence in alcoholics with a history of such behavior A second clinical trial performed at the University of Chicago found that fluoxetine reduced aggressive behavior in patients in intermittent aggressive disorder. A clinical trial found that fluoxetine reduced aggressive behavior in patients with borderline personality disorder. These results are indirectly supported by studies demonstrating that other SSRIs can reduce violence and aggressive behavior. A NBER study examining international trends in antidepressant use and crime rates in the 1990s found that increases in antidepressant drug prescriptions were associated with reductions in violent crime.
Contraindications include prior treatment (within the past fortnight) with MAOIs such as phenelzineand tranylcypromine, due to the potential for serotonin syndrome. Its use should also be avoided in those with known hypersensitivities to fluoxetine or any of the other ingredients in the formulation used. Its use in those concurrently receiving pimozide is also advised against.
Fluoxetine and norfluoxetine inhibit many isozymes of the cytochrome P450 system that are involved in drug metabolism possible. Both are potent inhibitors of CYP2D6 (which is also the chief enzyme responsible for their metabolism) and mild to moderate inhibitors of CYP1A2, CYP2B6, CYP2C9/2C19, and CYP3A4.They also inhibit the activity of P-glycoprotein, a type of membrane transport protein that plays an important role in drug transport and metabolism and hence P-glycoprotein substrates such as loperamide may have their central effects potentiated. This extensive effect on the body's pathways for drug metabolism creates the potential forinteractions with many commonly used drugs.
Its use should also be avoided in those receiving other serotonergic drugs such as monoamine oxidase inhibitors, tricyclic antidepressants, methamphetamine, MDMA, triptans, buspirone, serotonin-norepinephrine reuptake inhibitors and other SSRIs due to the potential for serotonin syndrome to develop as a result.
There is also the potential for interaction with highly protein-bound drugs due to the potential for fluoxetine to displace said drugs from the plasma or vice versa hence increasing serum concentrations of either fluoxetine or the offending agent.
The bioavailability of fluoxetine is relatively high (72%), and peak plasma concentrations are reached in 6 to 8 hours. It is highly bound to plasma proteins, mostly albumin and α1-glycoprotein.
Fluoxetine is metabolized in the liver by isoenzymes of the cytochrome P450 system, including CYP2D6. The role of CYP2D6 in the metabolism of fluoxetine may be clinically important, as there is great genetic variability in the function of this enzyme among people. Only one metabolite of fluoxetine, norfluoxetine (N-demethylated fluoxetine), is biologically active.
The extremely slow elimination of fluoxetine and its active metabolite norfluoxetine from the body distinguishes it from other antidepressants. With time, fluoxetine and norfluoxetine inhibit their own metabolism, so fluoxetine elimination half-life changes from 1 to 3 days, after a single dose, to 4 to 6 days, after long-term use. Similarly, the half-life of norfluoxetine is longer (16 days) after long-term use. Therefore, the concentration of the drug and its active metabolite in the blood continues to grow through the first few weeks of treatment, and their steady concentration in the blood is achieved only after four weeks. Moreover, the brain concentration of fluoxetine and its metabolites keeps increasing through at least the first five weeks of treatment. That means that the full benefits of the current dose a patient receives are not realized for at least a month since its initiation. For example, in one 6-week study, the median time to achieving consistent response was 29 days. Likewise, complete excretion of the drug may take several weeks. During the first week after the treatment discontinuation, the brain concentration of fluoxetine decreases only by 50%, The blood level of norfluoxetine 4 weeks after the treatment discontinuation is about 80% of the level registered by the end of the first treatment week, and 7 weeks after the discontinuation norfluoxetine is still detectable in the blood.
A PET study compared the action of a single dose of fluoxetine on exclusively heterosexual and exclusively homosexual men who attested that their past and present sexual behavior, desires, and fantasies were directed entirely toward women or men, respectively. The study found that in some areas of the brain the metabolic response in these two groups was different. "Both groups, however, did exhibit similar widespread lateralized metabolic responses to fluoxetine (relative to placebo), with most areas of the brain responding in the same direction." They "did not differ on behavioral measures or blood levels of fluoxetine".
Fluoxetine is a selective serotonin reuptake inhibitor and does not appreciably inhibit norepinephrine and dopamine reuptake. Nevertheless, Eli Lilly researchers found that a single injection of a large dose of fluoxetine given to a rat also resulted in a significant increase of brain concentrations of norepinephrine and dopamine.This effect may be mediated by 5HT2a and, in particular, 5HT2c receptors, which are inhibited by higher concentrations of fluoxetine. The Eli Lilly scientists also suggested that the effects on dopamine and norepinephrine may contribute to the antidepressant action of fluoxetine. In the opinion of other researchers, however, the magnitude of this effect is unclear. The dopamine and norepinephrine increase was not observed at a smaller, more clinically relevant dose of fluoxetine. Similarly, in electrophysiological studies only larger and not smaller doses of fluoxetine changed the activity of rat's norepinephrinergic neurons. Some authors, however, argue that these findings may still have clinical relevance for the treatment of severe illness with supratherapeutic doses (60–80 mg) of fluoxetine. Among SSRIs, 'fluoxetine is the least "selective" of all the SSRIs, with a 10-fold difference in binding affinity between its first and second neural targets (i.e., the serotonin and norepinephrine uptake pumps, respectively)'. Anything greater than a 10-fold difference results in insignificant activation of the secondary neuronal targets.
Besides its well-known effects on serotonin, fluoxetine also increases density of endogenous opioid receptors in the brains of rats. It is unclear if this occurs in humans, but if so it might account for some of fluoxetine's antidepressant and/or side effect profile.
Fluoxetine and norfluoxetine may be quantitated in blood, plasma or serum to monitor therapy, confirm a diagnosis of poisoning in hospitalized patients or assist in a medicolegal death investigation. Blood or plasma fluoxetine concentrations are usually in a range of 50–500 μg/L in persons taking the drug for its antidepressant effects, 900–3000 μg/L in survivors of acute overdosage and 1000–7000 μg/L in victims of fatal overdosage. Norfluoxetine concentrations are approximately equal to those of the parent drug during chronic therapy, but may be substantially less following acute overdosage, since it requires at least 1–2 weeks for the metabolite to achieve equilibrium.
Fluoxetine's mechanism of action is predominantly that of a serotonin reuptake inhibitor. Fluoxetine delays the reuptake of serotonin, resulting in serotonin persisting longer when it is released. Fluoxetine may also produce some of its effects via its weak 5-HT2C receptor antagonist effects. In addition, fluoxetine has been found to act as an agonist of the σ1-receptor, with a potencygreater than that of citalopram but less than that of fluvoxamine. However, the significance of this property is not fully clear.
Table 1: Binding affinity (Ki [nM]) of fluoxetine and norfluoxetine towards their molecular targets
Hoping to find a derivative inhibiting only serotonin reuptake, an Eli Lilly scientist, David T. Wong, proposed to retest the series for the in vitro reuptake of serotonin, norepinephrine and dopamine. This test, carried out by Jong-Sir Horng in May 1972, showed the compound later named fluoxetine to be the most potent and selective inhibitor of serotonin reuptake of the series. Wong published the first article about fluoxetine in 1974. A year later, it was given the official chemical name fluoxetine and the Eli Lilly and Company gave it the trade name Prozac. In February 1977, Dista Products Company, a division of Eli Lilly & Company, presented a new drug request to the U.S. Food and Drug Administration (FDA) for fluoxetine.
In May 1984, Germany’s regulatory agency (BGA) rejected Prozac as "totally unsuitable for treating depression". In May 1985, FDA’s (then) chief safety investigator, Dr. Richard Kapit, wrote: “Unlike traditional tricyclic antidepressants fluoxetine’s profile of adverse side effects more closely resembles that of a stimulant drug than one that causes sedation". He said "It is fluoxetine’s particular profile of adverse side-effects which may perhaps, in the future give rise to the greatest clinical liabilities in the use of this medication to treat depression".
Fluoxetine appeared on the Belgian market in 1986. After over a decade, the FDA gave its final approval in December 1987, and a month later Eli Lilly began marketing Prozac; annual sales in the U.S. reached $350 million within a year.
A controversy ensued after Lilly researchers published a paper titled "Prozac (fluoxetine, Lilly 110140), the first selective serotonin uptake inhibitor and an antidepressant drug" claiming fluoxetine to be the first selective serotonin reuptake inhibitor (SSRI). Two years later they had to issue a correction, admitting that the first SSRI was zimelidine developed by Arvid Carlsson and colleagues.
Eli Lilly's U.S. patent on Prozac (fluoxetine) expired in August 2001, prompting an influx of generic drugs onto the market. Prozac was rebranded "Sarafem" for the treatment of PMDD in an attempt to stem the post-patent decrease in Eli Lilly's sales of fluoxetine.
A meta-analysis published in February 2008 combined 35 clinical trials of four newer antidepressants (fluoxetine, paroxetine (Paxil), nefazodone (Serzone) and venlafaxine (Effexor) ). These antidepressants belonging to three different pharmacological groups were considered together, and the authors did not analyze them separately. The authors concluded that "although the difference [between the placebo and antidepressants] easily attained statistical significance", it did not meet the criterion for clinical significance, as used by the UK's National Institute for Health and Clinical Excellence, "for any but the most severely depressed patients". Some articles in the press using the titles "The creation of the Prozac myth" and "Prozac does not work in majority of depressed patients" presented these general findings about the relative efficacy of antidepressants and placebo as the findings about ineffectiveness of fluoxetine. In a follow-up article, the authors of the meta-analysis noted that "unfortunately, during its initial coverage, the media often portrayed the results as “antidepressants do not work”, which misrepresented our more nuanced pattern of findings".
As of April 2, 2010, fluoxetine is one of four antidepressant drugs that the FAA allows pilots to take. The others are sertraline (Zoloft), citalopram (Celexa), and escitalopram (Lexapro).
There has been research on possible effects of fluoxetine on marine life.
Brand names include ( † indicates discontinued brands):
Prozac has had numerous references to it in popular culture, including many books, movies, and songs.
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